INVESTIGADORES
MIRANDA Leandro Andres
congresos y reuniones científicas
Título:
Environmental effects on sex determination and fertility of fish, with special reference to temperature and atheriniforms
Autor/es:
STRUSSMANN CA; SOMOZA GM; MIRANDA LA; HATTORI RS; YAMAMOTO Y
Lugar:
Kona
Reunión:
Simposio; 7th International Symposium on Vertebrate Sex Determination.; 2015
Resumen:
Fishes
worldwide are under a growing threat from environmental problems such as habitat
degradation, eutrophication, acidification, climate change, pollutants and
endocrine disruptors, among
others. The ongoing trend of global warming and associated asymmetric thermal
fluctuations will likely impact developmental and physiological processes in fish
that include sex determination, gonadogenesis, and reproductive function.
Here we present a review of the current knowledge on the effects of temperature
on fish gonadal sex differentiation and fertility, with special reference to
Atheriniform fishes.
Atheriniforms,
often called ?silversides?, are found in marine, estuarine, and inland waters
around the globe, where they are ecologically and socioeconomically important. Several
Atheriniforms are known to have temperature-dependent sex determination (TSD). In
the genera Menidia and Odontesthes, the two most studied
groups, low and warm temperatures
favor the formation of females and males, respectively. In O. bonariensis, all-female and all-male populations are formed when
larvae are exposed to environmentally relevant temperatures of 17 and 29ºC,
respectively, between 1 and 5 weeks after hatching, a sensitiveness that is
unparalleled so far in other fish species. The sex ratios of young-of-the-year O. bonariensis in a natural population monitored
for 10 years were highly skewed (10-80% females) and variable from year to year,
and this variation was experimentally linked to TSD. We also demonstrated for
the first time the occurrence of heat-induced germ cell degeneration in fish, a phenomenon previously known only in males
of scrotal mammals (e.g. cryptorchidism).
Interestingly, fish females are also susceptible to heat-induced germ cell
degeneration. Partial or total loss of fertility in both sexes, tentatively
associated with past and prolonged exposure to heat, has been also observed in a
natural population.
Functional
studies have shown that TSD in our fish models involves temperature-induced
changes in gene expression, stress (cortisol) response, steroidogenesis, gonadal
apoptosis, and likely also brain and pituitary factors. We showed also that
histological gonadal sex differentiation in O.
bonariensis follows a peculiar chephalocaudal, left-to-right gradient
through the bilobed gonadal primordium, which is possibly related to TSD. In
contrast to O. bonariensis, sex
ratios in the congeneric O. hatcheri remain
relatively stable at 1:1 over a range of intermediate temperatures, suggesting
a relatively strong genetic component of sex determination. A major sex
determinant, amhy (Y-linked
anti-Müllerian hormone), has been described from this species. This was the
first report of a non-transcription factor, actually a hormone, being
implicated as the major sex determinant in vertebrates. This gene was recently found
and shown to be functional at intermediate temperatures in the TSD species O. bonariensis. These findings hint at the
coexistence of TSD and genotypic sex-determination (GSD) in fish. Apoptosis has
been implicated in germ cell degeneration and disappearance from gonads of fish
exposed to high temperatures.
Skewed sex
ratios, sex-reversals, and super-males (YY males) caused by temperature effects
on sex determination and partial to total loss of fecundity due to heat-induced
germ cell degeneration may become recurrent with further global warming and
climate change and cause demographic unbalances and even localized extirpations
in this group of fishes.